Fabrics having improved ballistic performance and processes for making the same

ABSTRACT

The invention provides fabrics having improved ballistic performance and processes for making the same. The fabrics include a network of consolidated multifilament yarns formed of high strength filaments. At least a portion of the high strength filaments of the yarns, are temporarily locked together to provide a substantially stable, flattened cross-sectional configuration to the yarns. The resultant fabrics are capable of absorbing an impact from a projectile, i.e., a bullet or shrapnel, directed toward the fabric and substantially decreasing its velocity. The fabric can also provide slippage or movement of the yarns relative to one another to dissipate the energy of impact of a projectile across a greater surface area of the fabric.

This application is a divisional of application Ser. No. 08/616,690,filed Mar. 15, 1996 now U.S. Pat. No. 5,788,907.

FIELD OF THE INVENTION

This invention relates generally to fabrics including high strengthfilaments, and more particularly to fabrics including high strengthfilaments which are useful for ballistic applications, and to processesof making the same.

BACKGROUND OF THE INVENTION

High strength fibers and filaments are widely used in ballisticresistant articles, such as bullet proof vests, curtains, mats,raincoats and umbrellas. Exemplary high strength fibers include aramidfibers, high molecular weight polyethylene fibers, nylon fibers, glassfibers, and the like. Various ballistic resistant articles which includehigh strength fibers made from materials such as high molecular weightpolyethylene are described, for example, in U.S. Pat. Nos. 4,820,568;4,748,064; 4,737,402; 4,737,401; 4,681,792; 4,650,710; 4,623,574;4,613,535; 4,584,347; 4,563,392; 4,543,286; 4,501,856; 4,457,985; and4,403,012.

For many ballistic resistant articles, such as vests, linings, and thelike, flexibility is a desired characteristic for comfort and mobilityof the wearer. In these and other applications, typically the ballisticresistant article includes a plurality of woven or knit fabrics formedof high strength fibers and/or filaments. For example, U.S. Pat. No.4,737,401 describes various woven fabrics made from high molecularweight extended chain polyethylene and polypropylene yarns, extendedchain polyvinyl alcohol yarns, and extended chain polyacrylonitrileyarns. U.S. Pat. No. 4,681,792 describes articles which include firstand second portions, the first portion comprising a plurality of layersof a first woven fabric and the second portion comprising a plurality oflayers of a second woven fabric. The fabrics of each of the first andsecond portions are selected to provide differing resistances todisplacement of the fibers therein.

U.S. Pat. No. 5,135,804 describes the application of heat and pressureto a network of high strength polyethylene fibers, including woven highstrength polyethylene fabrics, to provide an article havingconsolidation among the fibers to one of four levels. The fiber networkis treated at temperatures ranging from 100° C. to 160° C. (212° F. to320° F.) and pressures ranging from 0.5 to 1 MPa (in an autoclave) up to1 to 200 MPa (in a molding press). The patent indicates thattemperatures and pressures at the high end of these ranges, which deformthe fibers and form film-like structures, are required to achieveballistic-resistant articles.

These and other structures of high strength fibers can provide goodballistic performance when incorporated into a ballistic resistantarticle, such as a vest. However, to provide the desired degree ofresistance to displacement of the fibers or filaments upon impact of aprojectile, i.e., a bullet or shrapnel, typically multiple layers ofsuch fabrics must be used to construct the ballistic resistant article.Such articles can be heavy as a result. The use of multiple layers offabric can also compromise the flexibility of the resultant article.These factors can in turn reduce wearer comfort and mobility. Further,the use of a large number of fabric layers can increase the cost of sucharticles.

SUMMARY OF THE INVENTION

The present invention provides fabrics made from high strength filamentswhich can provide improved or enhanced ballistic protection as comparedto conventional fabrics of high strength filaments. For example, thefabrics of the invention can be used to construct ballistic resistantarticles which are substantially thinner, i.e., have fewer layers, thanconventional articles but which also exhibit comparable, and in somecases superior, ballistic protection. The fabrics of the invention canalso be used to construct ballistic resistant articles which haveimproved ballistic performance as compared to articles of substantiallyequal weights and construction formed of conventional fabrics. Furtherbenefits can include reduced trauma to the victim by reduced "backfacedsignature" i.e., the deformation of the fabric into the victim.

The fabrics of the present invention are formed of a network, preferablywoven, of consolidated multifilament yarns comprising high strengthfilaments. Within the yarns of the fabrics, at least a portion of thehigh strength filaments are temporarily locked together to provide asubstantially stable, flattened cross-sectional configuration to theyarns. As used herein, the term "substantially stable" indicates thatthe yarns can maintain their flattened configuration outside of thefabric network, believed due at least in part to some degree offilament-to-filament bonding within the yarns. However, althoughfilaments within the yarns can be locked together at least temporarily,the yarns maintain a substantially fibrous configuration, i.e., theyarns retain their individual identity and are not substantiallydeformed or film-like in appearance.

This fabric construction is advantageous in many regards. Theconsolidated, flattened multifilament yarns are believed to contributeto the impact resistance of the fabrics and resistance to displacementof filaments therein. The fabrics can be capable of receiving the impactof a projectile directed toward the fabric and of engaging theprojectile upon impact with the fabric to substantially decrease thevelocity thereof. However, the multifilament yarns are also capable ofslipping or moving relative to one another upon impact of a projectile.This is believed to be advantageous in distributing or dissipating theenergy of impact across a higher surface area of the fabric.

The fabrics preferably include high strength filaments having a tenacityof at least 7 grams/denier, a tensile modulus of at least about 150grams/denier and an energy-to-break of at least about 8 Joules/gram.Exemplary high strength filaments include extended chain polyolefinfilaments, aramid filaments, polyvinyl alcohol filaments,polyacrylonitrile filaments, liquid crystalline polymer filaments, S-2glass filaments, carbon filaments, high tenacity polyamide filaments,high tenacity polyester filaments, polybenzoxazole filaments, andmixtures thereof. Preferred filaments are extended chain polyethylenefilaments.

The present invention also provides processes for making the fabrics ofthe invention having enhanced ballistic performance. In this embodimentof the invention, a fibrous network of multifilament yarns includinghigh strength filaments is provided. Preferably the fibrous network is awoven fabric of such filaments. The yarns can be any of the conventionalhigh strength yarns known in the art, and typically have a substantiallycircular cross-sectional configuration.

In the processes of the invention, a precursor fibrous network ofmultifilament yarns including high strength filaments having a firstcross-sectional configuration is treated under conditions sufficient tochange or alter the cross-sectional configuration of the multifilamentyarns, i.e., to flatten the yarns. The flattened yarns can become moreuniformly aligned and/or spread out during such treatment so that theresultant fabric can have a substantially flat, smooth appearance.

Further, during such treatment, the yarns of the fabric can beconsolidated, i.e., at least a portion of the filaments therein aretemporarily locked together. This can impart substantial stability tothe flattened cross-section profile of the yarns, i.e., the yarns canmaintain their flattened profile when gently manipulated and removedfrom the fabric network. The conditions are also selected, however, tosubstantially preserve the fibrous nature of the yarns in the fabric,i.e., to retain their individual identity and to prevent substantialdegradation or melting of the yarns. Preferably, for woven fabrics ofhigh strength polyethylene filaments, the fabric is subjected topressure and heat conditions of about 300 Newtons and about 122° F., forexample, by calendering the fabric at a speed of about 27 meters perminute.

Compared to conventional ballistic resistant fabric, the fabrics of thepresent invention can advantageously provide a selected level ofballistic protection while employing a reduced weight of protectivematerial. Alternatively, the fabrics of the invention can provideincreased ballistic protection when the article has a weightsubstantially equal to the weight of a conventionally constructed pieceof flexible fabric type soft armor. Thus, such articles can bemanufactured with reduced weight, at reduced costs, and can maintain ahigh degree of flexibility. These factors can in turn can increasewearer comfort and mobility. Further, the fabrics are also useful in theconstruction of ballistic resistant articles which include ballisticresistant composite materials, such as composites formed of highstrength fibers imbedded in a polymeric matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which form a portion of the original disclosure of theinvention:

FIG. 1 is a perspective view of a conventional fabric including anetwork of high strength yarns; and

FIG. 2 is a perspective view of a fabric according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the invention, specificpreferred embodiments of the invention are described to enable a fulland complete understanding of the invention. It will be recognized thatit is not intended to limit the invention to the particular preferredembodiments described, and although specific terms are employed indescribing the invention, such terms are used in the descriptive sensefor the purpose of illustration and not for the purpose of limitation.It will be apparent that the invention is susceptible to variations andchanges as will be apparent from a consideration of the foregoingdiscussion and the following detailed description.

FIGS. 1 and 2 are perspective views of a conventional fabric 10 and of afabric 10' according to the invention, respectively. The fabrics 10 and10' comprise a network of high strength fibers or filaments as known inthe art and can be manufactured using any of the techniques known in theart for forming a fibrous coherent web of high strength fibers orfilaments, for example, by weaving, knitting, carding or other nonwovenfabric manufacturing techniques, and the like. The fabrics of theinvention are manufactured so as to as provide a high strength fabricsuitable for ballistic applications, and preferably are woven fabrics.

Fabrics 10' of the invention are useful in various ballisticapplications, i.e., as a component in any of the types of compositeproducts useful for ballistic protection. For example, the fabrics ofthe invention are useful as a layer in a multilayer article, includingbut not limited to, body armor, vests, linings, and the like.

As illustrated in FIGS. 1 and 2, fabrics 10 and 10' are woven fabricsformed from a plurality of multifilament yarns 12 and 12', respectively.As used herein, "filament" and "fiber" denotes a polymer which has beenformed into an elongate body, the length dimension of which is muchgreater than the transverse dimensions of width and thickness."Multifilament yarn" (also referred to herein as "yarn bundle") denotesan elongated profile which has a longitudinal length which is muchgreater than its cross-section and is comprised of a plurality or bundleof individual filaments or filament strands.

As illustrated in FIG. 2, the multifilament yarns or fiber bundles 12'of fabric 10' of the invention are flattened, for example, to asubstantially oval or oblong shape, as compared to the configuration ofthe multifilament yarns 12 of a conventional fabric 10. That is, theyarns tend to assume a less round or more flat profile as depicted inFIG. 2, in contrast to a substantially round or circular profile,illustrated in FIG. 1. Further, the flattened yarns can be moreuniformly aligned and/or spread out so that the resultant fabric canhave a substantially flat, smooth appearance and feel.

The yarns 12' of fabric 10' of the invention are also consolidated,i.e., at least a portion of the high strength filaments are temporarilylocked together within the yarns to substantially stabilize theflattened cross-sectional profile of the yarns. As used herein, theterms "substantially stable" or "substantially stabilized" indicate thatthe yarns can maintain their flattened configuration outside of thefabric network, for example, if the fabric is gently manipulated toremove yarns therefrom. Although not wishing to be bound by any theoryof the invention, it is believed that there is some degree offilament-to-filament thermal bonding within the yarns. Such bonding canbe temporary in the sense that discrete filaments within the yarns canbe removed one from another when a yarn is manipulated outside of thefabric network structure.

Fabrics formed of consolidated multifilament yarns having asubstantially flattened profile can provide several advantages in theballistic performance of the fabrics. Although not wishing to be boundby any explanation or theory of the invention, it is believed that themodified flattened profile of the yarns provides increased surface areacontact between individual yarns, as compared to conventionalsubstantially circular yarns. This in turn can provide resistance todisplacement of filaments and/or fibers in the yarns upon impact by aprojectile, i.e., a bullet or shrapnel. The term "resistance todisplacement" refers to the force required to displace a fiber orfilament in a given direction in the plane defined by the major face ofthe layer relative to an adjacent fiber or filament in the same layer.In preferred uses of the fabrics, the fabrics are incorporated in anarticle and the force which may displace the fiber or filament of agiven layer would be generated by a projectile, e.g., a bullet orshrapnel, impacting the fibrous layer. The ballistic performance of thefabrics is further enhanced by the consolidation of the yarns, and thetemporary locked structure of filaments within the yarns.

However, although a flattened yarn profile and consolidation betweenfilaments within the yarns are provided to impart increased resistanceto filament displacement, the fabrics of the invention also provide atleast some degree of slippage or movement of the yarns relative to oneanother. Thus, upon impact of a projectile on the fabric, the yarns canmove or slip relative to one another, thereby acting to absorb the forceof projectile impact and/or spread or dissipate the force of impactacross a higher surface area of the fabric.

High strength filaments which are useful in the fabrics of thisinvention include those formed of any of the high strength polymers asknown in the art. Exemplary high strength filaments include those havinga tenacity equal to or greater than about 7 grams per denier (g/d), atensile modulus equal to or greater than about 150 g/d and anenergy-to-break equal to or greater than about 8 Joules/gram (J/g).Tensile properties can be evaluated as known in the art, for example, bypulling a 10 inch (25.4 cm) fiber length clamped in barrel clamps at arate of 10 inches/minute (25.4 cm/min) on an Instron Tensile Tester.Preferred filaments are those having a tenacity at least about 10 g/d,more preferably at least about 15 g/d, and most preferably at leastabout 25 g/d; a tensile modulus at least about 200 g/d, more preferablyat least about 300 g/d, and most preferably at least about 400 g/d; andan energy-to-break at least about 20 J/g, more preferably at least about30 J/g, and most preferably at least about 35 J/g.

Types of filaments that meet the strength requirements include extendedchain polyolefin filaments, aramid filaments, polyvinyl alcoholfilaments, polyacrylonitrile filaments, liquid crystalline polymerfilaments, S-2 glass filaments, carbon filaments, boron filaments, hightenacity polyamide filaments, high tenacity polyester filaments,polybenzoxazole filaments, and mixtures thereof. Extended chainpolyethylene and extended chain polypropylene are the preferred extendedchain polyolefin filaments.

The extended chain polyolefins can be formed by polymerization ofα,β-unsaturated monomers of the formula R₁ R₂ C═CH₂, wherein R₁ and R₂are the same or different and are hydrogen, hydroxy, halogen,alkylcarbonyl, carboxy, alkoxycarbonyl, heterocycle or alkyl or aryleither unsubstituted or substituted with one or more substituentsselected from the group consisting of alkoxy, cyano, hydroxy, alkyl andaryl. For greater detail of such polymers of α,β-unsaturated monomers,see U.S. Pat. No. 4,916,000, hereby incorporated by reference.

U.S. Pat. No. 4,457,985, hereby incorporated by reference, generallydiscusses such high molecular weight extended chain polyethylene andpolypropylene filaments. In the case of polyethylene, suitable filamentsare those of molecular weight of at least 150,000, preferably at least300,000 more preferably at least one million and most preferably betweentwo million and five million. Such extended chain polyethylene (ECPE)filaments are known and may be grown in solution as described in U.S.Pat. No. 4,137,394 or U.S. Pat. No. 4,356,138, or may be a filament spunfrom a solution to form a gel structure, as described in German Off. 3004 699 and GB 20512667 and 2042414, and especially described in U.S.Pat. Nos. 4,413,110 and 4,551,296, also hereby incorporated byreference. Other high strength polyethylene filaments and techniquesknown for forming such filaments, including variations of the abovetechniques, can also be used in accordance with the present invention.Depending upon the formation technique, the draw ratio and temperatures,and other conditions, a variety of properties can be imparted to thesefibers.

The previously described highest values for tenacity, modulus andenergy-to-break are generally obtainable by employing these solutiongrown or gel filament processes. A particularly preferred high strengthfilament is extended chain polyethylene filament known as Spectra®,which is commercially available from Allied-Signal, Inc. As used herein,the term polyethylene refers to predominantly linear polyethylenematerials that may contain minor amounts of chain branching orcomonomers not exceeding 5 modifying units per 100 main chain carbonatoms, and that may also contain admixed therewith not more than about50 weight percent of one or more polymeric additives such asalkene-1-polymers, in particular, low density polyethylene,polypropylene or polybutylene, copolymers containing mono-olefins asprimary monomers, oxidized polyolefins, graft polyolefin copolymers andpolyoxymethylenes, or low molecular weight additives such asantioxidants, lubricants, ultraviolet screening agents, colorants andthe like, which are commonly incorporated by reference.

Similarly, highly oriented polypropylene of molecular weight at least200,000, preferably at least one million and more preferably at leasttwo million, may be used. Such high molecular weight polypropylene maybe formed into reasonably well-oriented filaments by techniquesdescribed in the various references referred to above, and especially bythe technique of U.S. Pat. Nos. 4,663,101 and 4,784,820, and publishedapplication WO 89 00213. Since polypropylene is a much less crystallinematerial than polyethylene and contains pendant methyl groups, tenacityvalues achievable with polypropylene are generally substantially lowerthan the corresponding values for polyethylene. Accordingly, a suitabletenacity is at least about 8 g/d, preferably at least about 11 g/d, andmore preferably at least about 15 g/d. The tensile modulus forpolypropylene is at least about 150 g/d, preferably at least about 200g/d, more preferably at least about 250 g/d, and most preferably atleast about 300 g/d. The energy-to-break of the polypropylene is atleast about 8 J/g, preferably at least about 40 J/g, and most preferablyat least about 60 J/g.

Useful aramid fibers include poly (para-amide) fibers having a modulusof at least about 400 grams/denier and tenacity of at least about 18grams/denier are useful in the fabrics of the invention, for example,poly(phenylenediamine terephthalamide) fibers produced commercially byDuPont Corporation under the trade name Kevlar® and having moderatelyhigh moduli and tenacity values.

High molecular weight polyvinyl alcohol filaments having high tensilemodulus are described in U.S. Pat. No. 4,440,711, hereby incorporated byreference. Preferred polyvinyl alcohol filaments will have a tenacity ofat least about 10 g/d, a modulus of at least about 200 g/d and anenergy-to-break of at least about 8 J/g, and particularly preferredpolyvinyl alcohol filaments will have a tenacity of at least about 15g/d, a modulus of at least about 300 g/d and an energy-to-break of atleast about 25 J/g. Most preferred polyvinyl alcohol filaments will havea tenacity of at least about 20 g/d, a modulus of at least about 500 g/dand an energy-to-break of at least about 30 J/g. Suitable polyvinylalcohol filament having a weight average molecular weight of at leastabout 200,000 can be produced, for example, by the process disclosed inU.S. Pat. No. 4,599,267.

In the case of polyacrylonitrile (PAN), PAN filament for use in thepresent invention are of molecular weight of at least about 400,000.Particularly useful PAN filament should have a tenacity of at leastabout 10 g/d and an energy-to-break of at least about 8 J/g. PANfilament having a molecular weight of at least about 400,000, a tenacityof at least about 15 to about 20 g/d and an energy-to-break of at leastabout 25 to about 30 J/g is most useful in producing ballistic resistantarticles. Such filaments are disclosed, for example, in U.S. Pat. No.4,535,027.

In the case of liquid crystal copolyesters, suitable filaments aredisclosed, for example, in U.S. Pat. Nos. 3,975,487; 4,118,372;and4,161,470, hereby incorporated by reference. Tenacities of about 15 to30 g/d, more preferably about 20 to 25 g/d, modulus of about 500 to 1500g/d, preferably about 1000 to 1200 g/d, and an energy-to-break of atleast about 10 J/g are particularly desirable.

The yarn can include filaments of more than one type of high strengthfilament. Preferably, however, the yarn is formed from filaments of onlyone type of high strength filament. The dpf of the yarn should be atleast 1.75, preferably at least 2.5, and most preferably 3.0.

If high molecular weight extended chain polyethylene filament is used toform the yarn, the denier of the resulting yarn should range from about100 to about 4800, preferably from about 200 to about 650. Especiallypreferred are 215, 375, 430 and 650 denier multifilament yarns. Thenumber of extended chain polyethylene filaments in a single yarn canrange from about 30 to 480, with about 60 to 120 filaments beingespecially preferred.

As noted above, preferably the fabrics of the invention are formed byforming a network of high performance fibers or filaments usingconventional techniques such as weaving, knitting, and the like, andpreferably by weaving. For woven fabrics, the weave pattern can be anyconventional pattern such as plain, basket, satin, crow feet, rib andtwill, and preferably is a plain weave pattern. It is to be noted thatif the network comprises yarns arranged in an overlapping arrangement(such as a plain or basket weave), the surface area of contact betweenadjacent yarns will increase, thus increasing the resistance ofdisplacement of filaments due in part to the increased frictional forcescreated by the increased contact surface area.

The fibers or filaments may be precoated with a polymeric material,preferably an elastomer based material, prior to being arranged in anetwork. A wide variety of suitable coating materials and techniques forcoating filaments using the same are well known in the art, for example,as described in U.S. Pat. Nos. 4,650,710, 4,737,401, and 5,124,195.

Any of the known matrix materials can also be used in manufacturing thefabrics of the invention, for example by coating the fabrics of theinvention with a matrix material. The use of fibrous networks withoutadditional matrix materials, however, can be advantageous, minimizing oreliminating the need for manipulating a separate matrix material.

When the fabrics of the invention are woven fabrics, the weaveconstruction used for the woven fabrics can be any conventional pattern,including 45×45, 34×34, and 56×56 plain weave pattern, with a 45×45plain weave pattern (45 yarn ends/inch in the warp direction; 45 yarnends/inch in the fill direction) being preferred.

Fabrics of the present invention that can be formed from the yarn mayinclude only one type of high strength filament, preferably highmolecular weight extended chain polyethylene. It is also contemplatedthat a fabric could include a second type of filament such as anotherhigh strength filament, or a filament that improves the feel orstretchability of the fabric such as nylon, polyester, spandex,polypropylene, cotton, silk, etc. For example, extended chainpolyethylene filaments can be used for the warp yarn and the secondfilament could be used for the fill yarn, or vice versa. Regardless ofwhat type of filament is used for the second filament, what is importantto the strength of the fabric is that it includes yarn of high strengthfilaments in either the warp or fill direction. If the fabric is formedfrom extended chain polyethylene exclusively, the filament used in onedirection (e.g., the warp) may be of a different tenacity, modulus,filament number, filament or total denier, twist than the filament usedin the other direction (e.g., the fill).

To make the fabrics of the invention, a network of multifilament yarnsincluding high strength filaments is provided. The filaments can beformed of any of the high strength polymers known in the art, such asthose described above. The cross-section of the fibers or filaments ofprecursor fabrics can vary widely. Typically such fibers or filamentshave a circular or substantially circular cross-section. Filamentshaving other cross-sections, for example, oblong, irregular or regularmulti-lobed, and the like, can also be used so long as the fibers orfilaments are capable of being flattened as described below.

The precursor fabric is subjected to conditions of pressure andtemperature sufficient to provide the enhanced or improved ballisticresistant fabrics of the invention. In this regard, sufficient pressureand temperature are applied to the precursor fabric to alter or changethe profile of the yarns therein from a first cross-section, typicallysubstantially circular shape as illustrated in FIG. 1, to a more flatshape as illustrated in FIG. 2. This, in turn, increases the surfacearea contact of the yarns, as described above, and can provide improvedprojectile penetration resistance. It is also to be noted that thecross-sectional configuration of discrete filaments of the multifilamentyarns can also change, for example, to provide yarns having a pluralityof flattened filaments about the periphery of the yarn. The pressure andtemperature applied to the fabric should not be so great, however, so asto substantially modify or destroy the fibrous nature of the yarns.

Sufficient pressure and temperature are also applied to the fabric toconsolidate the yarns and temporarily lock together at least a portionof the filaments therein to substantially stabilize the flattenedprofile of the yarns. It is believed that appropriate pressure andtemperature conditions can soften the polymer of the filaments andinduce some degree of filament-to-filament adhesion or bonding withinthe fiber bundles. However, fabric treatment conditions, i.e., pressureand/or temperature, should not be such that the polymer substantiallysoftens or melts, thus compromising the discrete individual identity andfibrous nature of the yarns. It is also to be noted that as illustratedin FIG. 2, pressure and temperature conditions can also be selected toimpart a substantially stable, crimped structure to the yarns of thefabrics at their cross-over or contact points, which can be retained bythe yarns outside of the fabric network.

Thus, pressure and temperature conditions are selected to alter, i.e.,flatten, yarn profile and to provide some degree of yarn consolidation,without substantially compromising or impairing the individual identityof the yarns or the ability of the yarns to slip upon impact by aprojectile.

To provide a consolidated, flattened yarn profile, yet also maintainslippage of the discrete yarns, the inventors have found that precursorfabrics can be calendered by directing the fabric between the nip formedby cooperating calender rolls, preferably a pair of smooth calenderrolls. The operating pressure and temperature of the calender rollsshould be adjusted to a pressure and surface temperature such that theyarn profiles are altered, i.e., flattened, and that the filaments ofthe yarns are thermally activated to temporarily lock the filamentstogether, thereby substantially stabilizing the flattened profile of theyarns. On the other hand, the pressure and heat transfer conditions areadvantageously maintained to avoid substantial thermal degradation ormelting of the yarns which are present within the fabric, and to avoidfilm formation.

As the skilled artisan will appreciate, calendering conditions includingpressure and temperature of the rolls can vary according to theparticular polymer composition of the filaments used and can bedetermined based upon the knowledge of the skilled artisan.Advantageously, for fabrics manufactured using high density polyethyleneas described above, the calender rolls are set to apply a pressure fromabout 290 to about 310, preferably about 300, Newtons, and a temperaturefrom about 113° F. to about 131° F. (about 45° C. to about 55° C.),preferably about 122° F. (50° C.) to the fabric. The fabric can be fedthrough the rolls at a speed of about 22 to 30 meters per minute,preferably about 27 meters per minute.

As will be appreciated by the skilled artisan, the use of heatedpressure rolls may result in some minor degree of yarn deformation andloss of individual fibrous identity due to partial fusion or melting ofthe polymer in one or more yarns. However, the fabric is primarilytreated as described above, and any thermal fusion or film formationthat may occur is minimal.

As the skilled artisan will appreciate, various sizing agents and otherprocessing aids can be present on the yarns of fabric to assist inprocessing the yarns to form the fibrous network. Advantageously thefabrics of the invention are treated, i.e., scoured, prior tocalendering to remove yarn lubricants and other processing agents on theyarns of the fabric using conventional scouring processes and solutions.The fabric can be scoured in water at temperatures from 75° F. to 115°F. (24° C. to 46° C.) in a bath pass process and dried at temperaturesless than about 160° F. (71° C.). This prepares the fabric substrate forsubsequent treatment with water repellent, as described below.

The fabrics of the invention can also be treated with any of the typesof agents known in the art for imparting a desired property to thefabric. For example, advantageously, a hydrophobic agent is applied tothe fabric to impart water repellency properties to the fabric. It isbelieved that the application of a water repellent agent to the fabriccan prevent water from promoting yarn slippage on impact with aprojectile. The hydrophobic agent can be applied to the fabric before orafter calendering, and preferably is applied prior to calendering. Anyof the various hydrophobic agents and processes for applying the sameknown in the art can be used.

Multilayer fabric articles, including a plurality of fabric layersarranged in any of the forms, numbers, etc., as known in the art, can beconstructed using the fabrics of the invention. The fabrics of theinvention are particularly useful as components of "soft" armor, whichis typically a flexible, multiple layer structure. The fabrics of theinvention can also be used in constructing vests, linings, and otherarticles of clothing comprising multiple layers of fabric.

It is convenient to characterize the geometries of such multilayerfabric structures by the geometries of the fibers or filaments therein.One such suitable arrangement is a plurality of layers in which eachlayer comprises a network of fibers or filaments and successive layersof such fabrics are rotated with respect to the previous layer. Anexample of such a multilayer fabric structure is a five layeredstructure in which the second, third, fourth and fifth layers arerotated +45°, -45°, 90°, and 0°, with respect to the first layer, butnot necessarily in that order. Another example is a fabric whichincludes fabric layers rotated 90° with respect to each other.

Multilayer fabric articles of the invention can vary with regard todensity, number of fabric layers, etc. The specific weight of themultilayer fabric article can be expressed in terms of areal density(AD). This areal density corresponds to the weight per unit area of themultiple layer structure. The multilayer fabric articles of theinvention can have good flexibility and fewer fabric layers, and thusincreased comfort at reduced cost. These properties can be coupled withexcellent ballistic protection, i.e., ballistic properties equal to, andsurpassing, a multilayer fabric article of the same weight,construction, number of layers, etc. formed of non-calendered fabrics.

The fabrics of the invention can also be incorporated as components ofother types of composite materials to provide the same types ofbenefits, i.e., reduced number of fabric layers, reduced weight andcost, increased comfort, improved ballistic performance, etc. Forexample, the fabrics of the invention can be used in combination withcomposites of high strength polyethylene fibers in a polymeric matrix,generally known in the art as Spectra® Shield, available commerciallyfrom Allied Signal, Inc.

The present invention will be further illustrated by the followingnon-limiting examples.

EXAMPLE 1 Preparation of Fabric

A plain weave fabric having 45 ends/inch in both the warp and filldirection was prepared from a high molecular weight polyethylene yarnavailable from Allied Signal, Inc. under the trade designation Spectra®.The warp yarn was twisted about 2 TPI (turns per inch), beamed, andwoven on a Dornier loom. After weaving, the yarn lubricants were removedby washing in hot water (75° F. to 115° F.). Thereafter, a waterrepellent agent Zonyl D available from DuPont was applied to the wovenfabric, and the fabric was passed between the nip of heated cooperatingpressure rolls at a speed of about 27 meters per minute (m/m). Thecalender rolls were set to a pressure of about 300 Newtons and atemperature of about 122° F. The resultant fabric had a substantiallysmooth, flat appearance, and the yarns within the fabric has a flattenedappearance.

A comparative fabric was also prepared as described above, except thatthe fabric was not calendered.

EXAMPLE 2 Ballistics Performance

A multilayer fabric target (or shot pack) was prepared using the fabricof the invention as described in Example 1 above (Sample A). Acomparative shot pack was also prepared, using the non-calenderedcomparative fabric of Example 1 (Sample B). The shot packs included 45layers of fabric, with a total areal density (AD) of 4.1 kg/m².

The fabric targets were one and one-half foot (27 inches) square andwere tested against 9 mm full metal jacketed bullets to obtain a V₅₀value for each pack. Most screening studies of ballistic compositesemploy a 9 mm full metal jacketed bullet of specified weight (124grains), hardness and dimensions (Mil. Spec. MIL-STD-662E (ORD)). Theprotective power of a structure is normally expressed by citing theimpacting velocity at which 50% of the projectiles are stopped and isdesignated the V₅₀ value.

To compare structures having different V₅₀ values and different arealdensities, the following examples state the ratios of the kinetic energy(Joules) of the projectile at the V₅₀ velocity, to areal density of thefabric (kg/m²). This ratio is designated as the Specific EnergyAbsorption (SEA).

Ballistic results are set forth in Table 1 below:

                  TABLE 1    ______________________________________              Fabric AD                       Target AD  V.sub.50                                        SEA    SAMPLE    (kg/m.sup.2)                       (kg/m.sup.2)                                  (ft/sec)                                        (J/m.sup.2 /kg)    ______________________________________    A         4.10     3.66       1.571 383    B         4.10     3.66       1.477 360    ______________________________________

As illustrated by the data in Table 1, the fabrics of the inventionprovide several advantages over a composite fabric formed ofnon-calendered fabric layers. The fabrics of the invention can providean article up to 25% thinner than a comparative article having a muchhigher V₅₀ value. Further, for articles of substantially equal weightsand construction, the fabrics of the invention can provide V₅₀ values upto 70 ft./sec. higher. Further benefits can include reduced trauma tothe victim by reduced "backfaced signature" i.e., the deformation of thefabric into the victim.

EXAMPLE 3 Fabric Performance in Combination with Spectra® Shield

Multiple layers of fabric of the invention as described in Example 1above are combined with a composite material available from AlliedSignal Inc. as Spectra® Shield, which includes polyethylene fibers in apolymeric matrix. The resultant article including the fabric layers ofthe invention and the Spectra® Shield product are also evaluated withregard to ballistic performance. The results indicate that the fabricsof the invention are also useful in combination with other ballisticresistant materials. The articles of the invention can provide ballisticprotection equal to and better than conventional composite materials,i.e., can exhibit excellent projectile penetration resistance andmultiple hits and fragment performance. Such articles can also besubstantially thinner and weigh and cost less.

The foregoing examples are illustrative of the present invention and arenot to be construed as limiting thereof. The invention is defined by thefollowing claims, with equivalents of the claims to be included therein.

That which is claimed is:
 1. A calendered fabric comprising a network ofconsolidated multifilament yarns comprising high strength filaments, atleast a portion of said high strength filaments being temporarily lockedtogether within said yarns to provide a substantially stable flattenedcross-sectional configuration to said yarns and wherein said yarns havea substantially stable, crimped structure at their cross-over points. 2.The fabric of claim 1, wherein said multifilament yarns havesubstantially individual fibrous identities.
 3. The fabric of claim 1,wherein said high strength filaments have a tenacity of at least 7grams/denier, a tensile modulus of at least about 150 grams/denier andan energy-to-break of at least about 8 Joules/gram.
 4. The fabric ofclaim 1, wherein said high strength filaments are selected from thegroup consisting of extended chain polyolefin filaments, aramidfilaments, polyvinyl alcohol filaments, polyacrylonitrile filaments,liquid crystalline polymer filaments, glass filaments, carbon filaments,high tenacity polyamide filaments, high tenacity polyester filaments,polybenzoxazole filaments, and mixtures thereof.
 5. The fabric of claim4, wherein said high strength filaments are extended chain polyethylenefilaments.
 6. The fabric of claim 1, wherein said fabric is a wovenfabric.
 7. The fabric of claim 6, wherein said woven fabric comprises afill yarn and a warp yarn and at least one of said fill yarn and saidwarp yarn includes said high strength filaments.
 8. The fabric of claim7, wherein said fill yarn and said warp yarns both comprise said highstrength filaments.
 9. The fabric of claim 1, wherein said network offlattened, consolidated multifilament yarns are capable of receiving animpact from a projectile directed toward said fabric and of engagingsaid projectile upon impact with said fabric to substantially decreasethe velocity thereof, and wherein said multifilament yarns also arecapable of slipping relative to one another upon impact of saidprojectile to substantially dissipate the energy of impact thereof. 10.A calendered woven fabric comprising a plurality of consolidatedmultifilament fill yarns and a plurality of consolidated multifilamentwarp yarns, each of said fill yarns and said warp yarns comprisingextended chain polyethylene filaments, at least a portion of said highstrength filaments being temporarily locked together within said fillyarns and said warp yarns to provide a substantially stable flattenedcross-sectional configuration to said fill yarns and said warp yarns,wherein said fabric of flattened consolidated multifilament fill andwarp yarns is capable of receiving an impact from a projectile directedtoward said fabric and of engaging said projectile upon impact with saidfabric to substantially decrease the velocity thereof, and wherein saidmultifilament fill and warp yarns also are capable of slipping relativeto one another upon impact of said projectile to substantially dissipatethe energy of impact thereof.
 11. A ballistic resistant multilayercomposite comprising as at least one layer a calendered network ofconsolidated multifilament yarns comprising high strength filaments, atleast a portion of said high strength filaments being temporarily lockedtogether within said yarns to provide a substantially stable flattenedcross-sectional configuration to said yarns and wherein said yarns havea substantially stable, crimped structure at their cross-over points.12. The composite of claim 11, further comprising as at least one layera composite formed of a plurality of high strength filaments distributedwithin a polymeric matrix.
 13. An article of manufacture comprising abody comprising as at least one layer a calendered network ofconsolidated multifilament yarns comprising high strength filaments, atleast a portion of said high strength filaments being temporarily lockedtogether within said yarns to provide a substantially stable flattenedcross-sectional configuration to said yarns and wherein said yarns havea substantially stable, crimped structure at their cross-over points.14. The article of claim 13, wherein said article is a vest.
 15. Afabric produced by the process comprising:providing a network ofmultifilament yarns having a first cross-sectional configuration, atleast a portion of said multifilament yarns comprising high strengthfilaments; and calendering said network to apply heat and pressure tosaid network under conditions sufficient to consolidate said yarns andto temporarily lock together at least a portion of said high strengthfilaments within said yarns to provide a second, substantially stableflattened cross-sectional configuration to said yarns.
 16. A fabricproduced according to the process comprising:calendering a woven fabriccomprising a network of multifilament yarns having a firstcross-sectional configuration, at least a portion of said multifilamentyarns comprising high strength filaments, at a pressure ranging fromabout 290 to 310 Newtons, a temperature ranging from about 45 to 55° C.,and a speed ranging from about 22 to 30 meters per minute, toconsolidate said yarns and to temporarily lock together a portion ofsaid high strength filaments within said yarns to provide a second,substantially stable flattened cross-sectional configuration to saidyarns.